Heating, ventilation and air conditioning (HVAC) units are used to control desired air conditions inside of interior building spaces. Typical HVAC products require an air testing and balancer technician in order to measure and control the fresh air quantity entering the indoor space. The technician is required to go onto the roof and to manually adjust the damper position of the unit until the airflow the unit reaches the amount required by the design of the engineer.
In some jurisdictions, the fresh air amount must be maintained at levels high enough to meet ASHRAE IAQ requirements, but not too much as to induce an increased load to the space. The test and balancing process may become more complicated for smarter units due to the complications of various controls and actuators. Additionally, Demand Control Ventilation (DCV) and exhaust fan interlock may further complicate this problem and multiple tests may be required. The methodical regulation of system fluid flow through an HVAC unit is described as balancing.
Depending on the type of building, the desired conditions required may vary and the system also be required to adapt to changing conditions both inside and outside. Some typical HVAC systems provide only reactive responses to changing conditions. For example, if pressure decreases, an outside air damper may be turned to an open position for a period of time. Reactive changes to the system may result in inefficiency and energy loss.
In some applications, certain conditions may require more careful control and balancing of the HVAC system. In particular, supermarkets or grocery stories have particular requirements, and these requirements may require carefully controlling space humidity levels. Moisture control is a central concern for a supermarket; too much moisture negatively affects the refrigeration system, and too little moisture negatively affects the fresh fruit and vegetables.
Various methods of balancing HVAC units and controlling air conditions in interior building spaces have been attempted.
Pargeter et al. (U.S. Pat. No. 6,792,767) describes a control system for a heating, ventilation, and air conditioning (HVAC) unit for controlling the humidity and temperature of interior building space at desired levels regardless of the outside temperature and humidity conditions. The control system employs a combination of modulated return air bypass, modulated capacity compressor, and modulating hot gas reheat. Pargeter does not describe a way of independently controlling the airflow across the cooling coil and the airflow bypassing the cooling coil for fine temperature and humidity adjustments.
Other patents that relate to the general field of HVAC systems include:    US Patent Publication No. 2013/0324027;    US Patent Publication No. 2012/0253534;    US Patent Publication No. 2011/0264280;    US Patent Publication No. 2011/0264275; and    U.S. Pat. No. 4,210,278.